The present invention relates generally to the homogenous grounding of a collection of inverters and thereby controlling the associated leakage current. More particularly, energy conversion systems and methods of the present invention relate to the homogenous grounding of a plurality of multi-level inverters and applying corrective actions to associated subsystems based on detected leakage current through a common grounding point.
PWM-based energy conversion devices are electrical devices capable of transferring electrical energy from an input source (generally DC in inverter systems) to an output source (generally AC in inverter systems). It is common practice to perform grounding connections with respect to both of the source (for example, a DC panel PV array) and the destination (for example, an electrical motor) to prevent degradation phenomena to the source/destination machines. One common example in the photovoltaic industry is the need to ground the photovoltaic (PV) array (positive or negative terminal) to prevent solar panel degradations due to the charging of the parasitic capacitance with respect to ground. In other situations, for example an electrical motor drive, the motor frame is connected to ground to prevent an erosion effect of the rotor cage due to leakage currents through the internal bearings.
Grounding operations are typically simple for a single machine but some problems could arise where, for example, a collection of devices are sharing the same AC output. In this case, a multiple grounding process will need to use special isolation techniques to avoid huge recirculation currents between the electrical machines involved in the energy conversion process. A typical example in the photovoltaic industry involves parallelization on the same AC grid output of multiple inverters that use different DC PV array sources and that must be uniformly (positive or negative) grounded. In this scenario, to prevent huge current recirculation, a multiple winding AC transformer will be needed to ensure galvanic isolations between the inverters respect ground potential.